Elemental Sulfur Corrosion of Mild Steel at High Concentrations of Sodium Chloride

                                                                     

ELEMENTAL SULFUR CORROSION OF MILD STEEL AT HIGH CONCENTRATIONS OF SODIUM CHLORIDE

Haitao Fang, David Young, Srdjan Nešić
Institute for Corrosion and Multiphase Technology

342 West State Street

Ohio University, Athens, Ohio 45701, USA ABSTRACT
A primary source of elemental sulfur in sour gas wells is the oxidation of hydrogen sulfide.   This may occur as a result of ingress of oxygen.  Typically, elemental sulfur is carried by the sour gas through the pipeline. However, as pressures and temperatures decrease, sulfur will deposit on the pipeline.  In aqueous conditions, contact of solid sulfur with mild steel can result in the onset of catastrophic corrosion processes. According to previous research, high salt concentration was suspected to have a significant effect on the corrosion process.
The objective of this project is to study the effect of high sodium chloride concentration on elemental sulfur corrosion of mild steel. In initial experiments, elemental sulfur hydrolysis and sulfur-mild steel corrosion at salt free conditions were investigated.  Sulfur was found to react with water at temperatures of greater than 80^oC, resulting in significant acidification of the corrosion solutions.  Iron sulfide films/scales readily formed on the surface of the steel.  These were analyzed by infinite focus microscopy (IFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD).  It was also determined that elemental sulfur can cause localized corrosion of mild steel when they are in direct contact with each other.

Keywords: Elemental sulfur, mild steel, high sodium chloride concentration, iron sulfide, sulfur hydrolysis, localized corrosion.